Floyd Mayweather Jr. (left) throws a left to the face of Robert Guerrero in their WBC welterweight title bout at the MGM Grand Garden Arena. Al Bello, Getty Images

Robert Guerrero in the ring before the start of the WBC Welterweight title fight against Floyd Mayweather (not pictured) at the MGM Grand Garden Arena. Mayweather won. Jayne Kamin-Oncea, USA TODAY Sports

Floyd Mayweather Jr. stands in the ring before taking on Robert Guerrero in their WBC welterweight title bout at the MGM Grand Garden Arena. Al Bello, Getty Images